A jammed actuator, lack of pressure in the system, or uncontrolled load drop – any of these symptoms can indicate a failure of the control system's heart, the spool solenoid valve.
In the previous BRhydraulic blog post, we discussed coil selection in detail. Today, we're taking a closer look at the directional control valves themselves. Since the CETOP 3 standard (also known as NG6 or size 06) is the most popular connection type worldwide, we will focus on it. How do you decipher complex manufacturer codes and choose a replacement that will get your machine running?
Here are 4 steps you need to take.
1. Make sure it's a CETOP 3 (NG6) standard
The CETOP standard (a European committee of drive manufacturers) guarantees valve interchangeability regardless of the manufacturer (e.g., Rexroth, Ponar, Argo Hytos, or Vickers). If your damaged directional control valve is NG6 size (CETOP 3), it means that the spacing of the four mounting holes and oil ports (P, T, A, B) on the subplate is standardized.
The NG6 size typically allows for flow rates up to 60-80 l/min at a maximum operating pressure of 315-350 bar. If these parameters match your machine, you can safely select a replacement from any reputable brand.
2. Identify the spool schematic (Most important step!)
This is where customers make the most mistakes. The external appearance of a two-coil directional control valve tells you nothing about how the oil behaves inside. You must check the schematic engraved on the nameplate (usually a letter symbol, e.g., E, G, J, H).
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Type E spool (e.g., 4WE6E): In the central (neutral) position, all ports (P, T, A, B) are closed. The actuator is locked in place, and the pump operates at full pressure to the relief valve. The most common choice in classic systems.
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Type G spool (e.g., 4WE6G): In the central position, the working ports (A, B) are closed, but the supply port (P) is connected to the tank return (T). This relieves the pump when the machine is not moving.
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Type J spool (e.g., 4WE6J): The supply port (P) is closed, but the actuator ports (A, B) are connected to the tank (T). Used when the actuator in the neutral position must "float" freely (e.g., under external forces).
BRhydraulic Tip: Installing a Type E spool instead of a G can cause the system oil to immediately overheat and destroy the pump! Always check the schematic letter.
3. Spool return type (Spring or detent?)
Most CETOP valves use centering springs. This means that when you cut power to the coil, the spring immediately pushes the spool back to the central (safe) position. However, there are also so-called impulse valves (without springs). A short electrical pulse moves the spool, which then remains in that position until a pulse is applied to the second coil. Before purchasing, make sure what type of control your PLC or relay system requires.
4. Choose the appropriate coil voltage (and plug)
If you are purchasing a complete valve with coils (not just the body), ensure that the voltage matches the machine's power supply system. The most common are 12V DC and 24V DC (mobile, agricultural machinery) and 230V AC (stationary industrial). Also remember to choose electrical plugs with LED diodes, which greatly facilitate subsequent diagnostics (you can immediately see if power is actually reaching the valve).
🛠️ The Golden Rule of Maintenance: Cleanliness!
Even the highest-class 4WE6 directional control valve will seize within a few hours if contaminated oil enters it. The spool's fit tolerances in the body are measured in micrometers. Before installing a new valve from the BRhydraulic offer, be sure to change the filters and make sure that the failure of the previous component was not caused by metal shavings from a seizing pump.
If you need help selecting a replacement for a damaged valve, check out our range of 4WE6 solenoid valves or contact our technical support!
We also remind you that our proprietary, free calculator can help you quickly calculate parameters (such as actuator speed or pump power).
